The present invention relates to an electronic apparatus such as a portable computer, and more particularly to a structure for cooling the heat-generating components provided in such an electronic apparatus.
In recent years, portable electronic apparatuses, represented by book-like portable computers and mobile information apparatuses, have been developed. Each of these apparatuses incorporates a high-speed MPU (Microprocessing Unit) and has various functions in order to process multimedia information, such as characters, speech, sound, and images. The higher the integration density it has, and the more functions it performs, the more electric power the MPU consumes while operating. The more electric power it consumes, the more heat the MPU generates. In the case of a portable computer incorporating an MPU, the heat generated by the MPU must be radiated efficiently from the MPU in the housing of the portable computer. It is therefore absolutely necessary to provide a cooling unit in the housing to cool the MPU positively.
A conventional system for cooling an MPU will be described, with reference to FIG. 25. As shown in FIG. 25, an MPU 2 is mounted on a circuit board 1 provided in the housing (not shown) of a portable computer. A cooling unit 3 for cooling the MPU 2 is provided on the upper surface of the circuit board 1.
The cooling unit 3 comprises a flat heat sink 4 and an electric fan device 5. The heat sink 4 is made of metal having high thermal conductivity, such as aluminum alloy. The heat sink 4 is thermally connected to the MPU 2. Hence, heat can be conducted from the MPU 2 to the heat sink 4. The heat sink 4 has a number of radiation fins 6 on the upper surface, which faces away from the MPU 2. The radiation fins 6 extend in the direction of thickness of the heat sink 4 and are exposed in the housing of the portable computer.
The electric fan device 5 is arranged at one end of the heat sink 4. The device 5 comprises a fan casing 7 and a fan 8. The fan casing 7 has an air passage 7a. The fan 8 is provided in the air passage 7a. The fan device 5 is vertically positioned and secured to the heat sink 4, and the rotation axis O1 of the fan 8 extends horizontally. The inlet end of the air passage 7a faces the radiation fins 6, whereas the outlet end of the passage 7a faces the exhaust port of the housing.
When the fan 8 is driven and rotated, a stream of cooling air is generated in the housing, flowing toward the heat sink 4. The cooling air then flows along the heat sink 4 and the radiation fins 6. Finally, the air is exhausted from the housing through the exhaust port of the housing. The convection of cooling air, occurring in the housing, cools the heat sink 4. Thus, the heat transmitted from the MPU 2 to the heat sink 4 is expelled from the housing.
A prominent commercial value of portable electronic apparatuses, such as portable computers, is their portability. This is why the housings of portable computers are getting thinner and lighter recently, so that they may be put into bags and the like. The above-described cooling unit 3, which incorporated in the housing of the portable computer, should also be made thinner and lighter.
However, the conventional cooling unit 3 can hardly be rendered lighter for the following reason. As mentioned above, the heat sink 4 is cooled by virtue of the convection of cooling air. The cooling ability of the unit 3 is therefore determined by the surface area of the heat sink 4 and the flow rate of the cooling air supplied by the fan device 5. In order to increase the cooling ability, the heat sink 4 must be larger and more radiation fins 6 must be provided. Consequently, the cooling unit 3 must be heavier.
To make matters worse, the conventional cooling unit 3 must be rather thick. This is because the fan device 5 is vertically positioned and secured to the heat sink 4 and the rotation axis O1 of the fan 8 extends horizontally. The fan casing 7 inevitably project upward for a long distance from the heat sinks 4.
As a consequence, the higher the cooling ability of the unit 3, the thicker, larger and heavier the cooling unit 3 should be. Any portable computer that incorporates a thick cooling unit can hardly be as thin as is desired.